JP7706997B2 - Method for producing substrate with conductive layer - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act January 20, 2021 to January 22, 2021, Tokyo Big Sight (3-11-1 Ariake, Koto-ku, Tokyo), Tetsuya Yoneda and Hirotaka Muto demonstrated wired PTFE nanofiber at the 35th NEPCON JAPAN.

The present invention relates to a substrate with a conductive layer.

Flexible printed circuit boards have been known as flexible circuit boards. Although flexible printed circuit boards are more flexible than circuit boards that use a metal substrate such as copper, for example, the substrate is still too hard for use in wearable devices, and there has been a demand for circuit boards that use a substrate with greater flexibility.

In this regard, for example, Patent Document 1 discloses a flexible printed circuit board that uses expanded polytetrafluoroethylene (e-PTFE) as the substrate.

International Publication No. 2019/216883

Flexible printed circuit boards used in wearable devices and the like require not only flexibility but also breathability. However, conventional flexible printed circuit boards have room for improvement in terms of breathability.

In addition, flexible printed circuit boards sometimes use thermosetting conductive compositions to form conductive layers, but it has been found that when such thermosetting conductive compositions are used, conventional flexible printed circuit boards do not have sufficient heat resistance and end up shrinking due to heat. Furthermore, flexible printed circuit boards are sometimes used to mount electronic components, but it has been found that conventional flexible printed circuit boards cannot adequately withstand the high temperatures that occur during this mounting.

The present invention has been made in consideration of the above, and aims to provide a substrate with a conductive layer that is excellent in flexibility, breathability, and heat resistance.

Under these circumstances, the present inventors conducted extensive research to solve the above problems, and as a result, found that the above problems can be solved by the following configuration examples, and completed the present invention.
A configuration example of the present invention is as follows.

[1] A substrate that is a woven or nonwoven fabric containing nanofibers made of polytetrafluoroethylene (PTFE);
The substrate with a conductive layer has on the substrate a conductive layer formed from a conductive composition having a viscosity of 1 to 500 Pa·s at 25° C. and 50 rpm as measured by a rotational viscosimetry method, and satisfies the following requirement (1).
Requirement (1): The Gurley air permeability of the substrate with the conductive layer is 10 seconds/100 ml or less.

[2] The substrate with a conductive layer according to [1], wherein the conductive composition contains a conductive filler and a thermosetting resin.

[3] The substrate with a conductive layer according to [1] or [2], wherein the substrate has a basis weight of 10 to 200 g/ ^m2 before the conductive layer is formed.

According to the present invention, it is possible to provide a substrate with a conductive layer that is excellent in flexibility, breathability and heat resistance.
Furthermore, according to the present invention, a desired conductive layer can be formed on a substrate made of PTFE, which is inherently non-adhesive, and which will not peel off or break even after a bending test or the like. It is also possible to provide a substrate with a conductive layer that is less susceptible to deformation due to thermal shrinkage and makes use of the properties of PTFE, such as cleanliness, insulation, and low dielectric constant.
Furthermore, since the substrate with a conductive layer according to the present invention has excellent heat resistance as described above, the substrate with a conductive layer can be subjected to a sterilization treatment such as autoclave sterilization when used, for example, for healthcare applications.

<Substrate with conductive layer>
The substrate with a conductive layer according to the present invention (hereinafter also referred to as the "substrate with a conductive layer") has a substrate which is a woven or nonwoven fabric containing nanofibers made of polytetrafluoroethylene (PTFE), and a conductive layer formed on the substrate from a conductive composition having a viscosity of 1 to 500 Pa s at 25° C. and 50 rpm as measured by a rotational viscosimetry method, and satisfies the following requirement (1).
Requirement (1): The Gurley air permeability of the conductive layer-attached substrate is 10 sec/100 ml or less.

The Gurley air permeability of the conductive layer-attached substrate is 10 sec/100 ml or less, preferably 5 sec/100 ml or less, more preferably 1 sec/100 ml or less. The lower limit of the Gurley air permeability is not particularly limited, but is, for example, 0.1 sec/100 ml or more.
The present substrate with a conductive layer, which has a conductive layer on the substrate and has the above-mentioned Gurley air permeability, can be said to have excellent breathability and can be particularly suitably used in wearable devices, and further can be suitably used in devices used in the healthcare field, etc., which are used in close contact with the living body.
Specifically, the Gurley air permeability can be measured by the method described in the following examples.

The present substrate with a conductive layer may have a conductive layer on one of the main surfaces (the surface having the largest area) of the substrate, and may have conductive layers on both of the main surfaces of the substrate.
In the present substrate with a conductive layer, a substrate that is a woven or nonwoven fabric is used, and therefore a conductive layer (circuit) formed on one side can be connected to a conductive layer (circuit) formed on the back side or to electronic components, for example, by filling the voids in the substrate with a conductive composition.
The number of conductive layers formed on the substrate is not particularly limited, and the conductive layers may be appropriately provided depending on the conductive layers (circuits) to be formed.

The present substrate with a conductive layer is not particularly limited as long as it has a substrate and a conductive layer, and may have an insulating overcoat layer, or a conventionally known layer or member provided on a circuit board or the like for electronic components (e.g., sensors, switches, connectors, etc.).
The substrate and the conductive layer may be bonded via an adhesive layer or the like. However, since the effects of the present invention are more effectively exhibited and the substrate and the conductive layer can be sufficiently bonded even without the adhesive layer, it is preferable that the substrate and the conductive layer are in contact with each other (the conductive composition is formed directly on the substrate).

The present substrate with a conductive layer can be used in devices used in various fields. Since the present substrate with a conductive layer has excellent flexibility, for example, by disposing the present substrate with a conductive layer on a member having a complex shape, a circuit or the like can be easily formed on the member having the complex shape.
Furthermore, since the present substrate with a conductive layer has excellent flexibility and breathability, and further has excellent water repellency and is resistant to dirt, it can be particularly suitably used in wearable devices, and furthermore, it can be suitably used in devices used in the healthcare field, etc., which are used in close contact with the living body.

<Base material>
The substrate is a woven or nonwoven fabric containing polytetrafluoroethylene (PTFE) nanofibers, preferably a woven or nonwoven fabric made of PTFE nanofibers (only), and more preferably a nonwoven fabric made of PTFE nanofibers (only).
The woven or nonwoven fabric containing PTFE nanofibers is a substrate that is different from the expanded substrate having nodes.
Since the present substrate with conductive layer uses such a substrate, even if high temperatures (e.g., 200°C) are applied when forming the conductive layer or when mounting electronic components, the substrate is unlikely to shrink and has excellent heat resistance.

The thickness of the substrate may be appropriately selected depending on the application, but is preferably 1 μm to 500 mm, more preferably 3 to 100 μm, in order to easily obtain a substrate with a conductive layer having excellent flexibility.

The base material preferably has a basis weight of 10 to 200 g/m ² , more preferably 16 to 40 g/m ² .
When the basis weight of the substrate is within the above range, a substrate with a conductive layer can be easily obtained in which the conductive layer and the substrate are bonded with sufficient adhesive strength. This is presumably because, when the conductive layer is formed using a conductive composition containing a binder, the binder penetrates into the substrate and easily exerts its anchoring effect.
The weight per unit area tends to increase by extending the spinning time, increasing the number of spinning nozzles, and the like.

The nonwoven and woven fabrics are made by accumulating or weaving PTFE nanofibers into a sheet shape, and such nonwoven and woven fabrics may be made of a single layer or two or more layers made of different materials or fiber diameters.

The nonwoven fabric may be made by a variety of methods, including wet papermaking, water punching, chemical bonding, thermal bonding, spunbonding, needle punching, and stitch bonding. From the standpoints of heat resistance, mechanical properties, and solvent resistance, nonwoven fabrics made by the thermal bonding or spunbonding methods using self-melting fibers are preferred.

The PTFE nanofibers constituting the woven fabric may be monofilament yarn, multifilament yarn, or staple yarn. There are no particular limitations on the weaving method, and examples include plain weave, twill weave, satin weave, twenty-fiber weave, and tubular weave. There are no particular specifications for the weaving structure, yarn count, or yarn density.

The average fiber diameter (average fiber diameter) of the PTFE nanofibers constituting the nonwoven or woven fabric is preferably 500 nm to 1 μm.
When the average fiber diameter is within the above range, a nonwoven fabric or woven fabric exhibiting high flexibility can be formed, and the surface area of the fibers is increased, making it possible to easily obtain a substrate with a conductive layer in which the conductive layer and the substrate are bonded with sufficient adhesive strength, which is preferable in that the distribution uniformity of the fibers can be increased even when a thin nonwoven fabric or woven fabric is formed.

The average fiber diameter of the PTFE nanofibers constituting the nonwoven or woven fabric can be adjusted by appropriately selecting the conditions for forming the nanofibers. For example, when producing nanofibers by electrospinning, the average fiber diameter of the resulting nanofibers tends to be reduced by lowering the humidity during electrospinning, reducing the nozzle diameter, increasing the applied voltage, or increasing the voltage density.

The average fiber diameter is an average value calculated based on the results of observing the nanofiber (group) to be measured with a scanning electron microscope (SEM) (magnification: 10,000 times), randomly selecting 20 nanofibers from the SEM image, and measuring the nanofiber diameter (long axis) of each of these nanofibers.

The fiber diameter variation coefficient of the PTFE nanofibers constituting the nonwoven or woven fabric is preferably 0.7 or less, more preferably 0.01 to 0.5, as calculated by the following formula. When the fiber diameter variation coefficient is within the above range, the PTFE nanofibers have a uniform fiber diameter, and a substrate with a conductive layer in which the conductive layer and the substrate are bonded with sufficient adhesive strength can be easily obtained.
Coefficient of variation of fiber diameter=standard deviation/average fiber diameter (Note that “standard deviation” refers to the standard deviation of the fiber diameters of the 20 fibers.)

The fiber length of the PTFE nanofibers constituting the nonwoven or woven fabric is preferably 0.1 to 1000 mm, more preferably 0.5 to 100 mm, and even more preferably 1 to 50 mm.

The PTFE nanofibers are manufactured by, for example, electrospinning, melt spinning, melt electrospinning, spunbonding (meltblowing), wet, and spunlace methods. Nanofibers obtained by electrospinning have a small fiber diameter, and nonwoven or woven fabrics made from such nanofibers exhibit high flexibility.

When forming PTFE nanofibers using electrospinning, for example, a spinning solution containing PTFE and, if necessary, a solvent is used.
The content of PTFE in the spinning solution is preferably 5 to 80% by mass, and more preferably 10 to 70% by mass.

The solvent is not particularly limited as long as it can dissolve or disperse PTFE, and examples thereof include water, dimethylacetamide, dimethylformamide, tetrahydrofuran, methylpyrrolidone, xylene, acetone, chloroform, ethylbenzene, cyclohexane, benzene, sulfolane, methanol, ethanol, phenol, pyridine, propylene carbonate, acetonitrile, trichloroethane, hexafluoroisopropanol, and diethyl ether. These solvents may be used alone or in combination of two or more.
The solvent is contained in the spinning solution in an amount of preferably 10 to 90% by mass, more preferably 20 to 80% by mass.

The spinning solution may further contain additives other than PTFE, such as inorganic fillers, surfactants, dispersants, charge control agents, functional particles, adhesives, viscosity control agents, fiber forming agents, etc. These additives may be used alone or in combination of two or more.
In the spinning solution, when the solubility of PTFE in the solvent is low (for example, when the solvent is water), it is preferable to contain one or more fiber forming agents, since this makes it easier to maintain the PTFE in a fiber shape during spinning.

The fiber-forming agent is preferably an organic polymer having high solubility in a solvent, and examples thereof include polyethylene oxide, polyethylene glycol, dextran, alginic acid, chitosan, starch, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, cellulose, and polyvinyl alcohol.
The amount of the fiber-forming agent used, depending on the viscosity of the solvent and the solubility in the solvent, is, for example, 0.1 to 15% by mass, preferably 1 to 10% by mass in the spinning solution.

The spinning solution can be produced by mixing PTFE, a solvent, and, if necessary, additives, using a conventional method.

A preferred example of the spinning solution is the following spinning solution (1).
Spinning solution (1): A spinning solution containing 30 to 70% by mass, preferably 35 to 60% by mass, PTFE, 0.1 to 10% by mass, preferably 1 to 7% by mass, of a fiber-forming agent, and a solvent so that the total is 100% by mass.

The voltage applied during electrospinning is preferably 1 to 100 kV, more preferably 5 to 50 kV, and even more preferably 10 to 40 kV.

The tip diameter (outer diameter) of the spinning nozzle used for electrospinning is preferably 0.1 to 2.0 mm, more preferably 0.2 to 1.6 mm.

More specifically, for example, when the spinning solution (1) is used, the applied voltage is preferably 10 to 50 kV, more preferably 10 to 40 kV, and the tip diameter (outer diameter) of the spinning nozzle is preferably 0.3 to 1.6 mm.

After forming a nonwoven or woven fabric from the PTFE nanofibers, it is preferable to carry out a heat treatment. The heat treatment is usually carried out by heat treating the obtained nonwoven or woven fabric at 200 to 390°C for 30 to 300 minutes. This heat treatment can remove the solvent and fiber-forming agent remaining in the nonwoven or woven fabric.

As a method for producing the nonwoven fabric, a conventionally known production method can be adopted, and for example, the following method described in JP-A-2012-515850 can be mentioned.
Providing a spinning solution, preferably a spinning solution (1), comprising PTFE, a fiber former and a solvent and having a viscosity of at least 50,000 cP;
A step of spinning the spinning solution from a nozzle and forming fibers by electrostatic traction force;
collecting the fibers on a collector (e.g., a take-up spool) to form a precursor;
and calcining the precursor to remove the solvent and the fiber-forming agent to form a nonwoven fabric of PTFE nanofibers.

<Conductive Layer>
The conductive layer is not particularly limited as long as it is a layer having conductivity formed from a conductive composition, and is, for example, a circuit. The conductive composition is not particularly limited as long as it is a composition having a viscosity of 1 to 500 Pa·s at 25° C. and 50 rpm as measured by a rotational viscosimetry method, and a conventionally known composition can be used, and a conductive composition containing a conductive filler and a binder is preferred.
In the present invention, the term "conductive composition" means that a conductive layer obtained from the composition has a resistivity of less than 1× ¹⁰ Ω·cm. The resistivity can be calculated by measuring the resistance with a digital multimeter and using the following formula:
Specific resistance (Ω・cm)=R×S/l
[R: resistance value of the digital multimeter, S: cross-sectional area of the conductive layer, l: distance between electrodes]

The viscosity of the conductive composition measured by a rotational viscometer at 25° C. and 50 rpm is 1 to 500 Pa·s, preferably 10 to 100 Pa·s, and more preferably 10 to 50 Pa·s.
When the viscosity is within the above range, a substrate with a conductive layer can be easily obtained in which the conductive layer and the substrate are bonded with sufficient adhesive strength, even for a substrate made of PTFE, which is inherently non-adhesive. This is presumably because, when a conductive layer is formed using a conductive composition containing a binder having a viscosity within the above range, the binder penetrates into the substrate and is likely to exert its anchoring effect.

The conductive filler is not particularly limited, and any conventionally known filler can be used.
The conductive filler used in the conductive composition may be of one type, or may be of two or more types different in shape, size, material, and the like.

The material of the conductive filler is not particularly limited as long as it is a material having conductivity, and examples thereof include metals such as copper, silver, gold, platinum, tin, bismuth, zinc, indium, nickel, and palladium, alloys containing these metals, carbon black, and graphite. Among these, copper, silver, and carbon black are preferred.
The conductive filler may be a filler obtained by plating the surface of a material with the metal or alloy.

The shape of the conductive filler is not particularly limited, and examples include chunks, spheres, flakes, needles, fibers, dendrites, and coils.

The median diameter (D50) of the conductive filler measured by the laser diffraction scattering method (microtrack method) is preferably 5 to 30 μm, since this allows a composition with excellent paintability to be obtained and a conductive layer with excellent conductivity to be easily obtained.

The content of the conductive filler is preferably 60 to 95% by mass, and more preferably 65 to 93% by mass, relative to 100% by mass of the conductive composition, in order to easily obtain a conductive layer with excellent conductivity.

The binder is not particularly limited, and is preferably one that can hold the conductive filler.
The conductive composition may contain one or more binders.

The binder is not particularly limited, and examples thereof include thermoplastic resins such as polyester resin, acrylic resin, butyral resin, and thermoplastic imide resin; epoxy resins such as bisphenol A type, bisphenol F type, and novolac type, epoxy compounds such as liquid epoxy compounds, polyester resins such as unsaturated polyester resin, urethane resin, phenol resins such as resol type and novolac type, imide resin, and thermosetting resins such as silicone rubber; and elastomers such as styrene-based elastomers, olefin-based elastomers, polyester-based elastomers, polyurethane-based elastomers, polyamide-based elastomers, and silicone-based elastomers.
Among these, thermosetting resins are preferred because they cure in a state in which they have soaked into the substrate, and because of the anchor effect, they can easily provide a substrate with a conductive layer having superior adhesive strength between the conductive layer and the substrate.

The content of the binder is preferably 5 to 35 parts by mass, and more preferably 7 to 20 parts by mass, per 100 parts by mass of the conductive filler, in order to adequately hold the conductive filler and easily obtain a conductive layer that has excellent shape retention and conductivity.

The conductive composition preferably contains one or more solvents from the viewpoint of paintability, etc., and the solvent is not particularly limited, but examples thereof include alcohol-based solvents such as methanol, ethanol, isopropyl alcohol, butyl carbitol, butyl cellosolve, and propylene glycol monomethyl ether; aromatic solvents such as toluene and xylene; ketone-based solvents such as methyl isobutyl ketone; and ester-based solvents such as methyl acetate, ethyl acetate, and butyl carbitol acetate.

In addition to the above components, the conductive composition may contain conventionally known additives, if necessary, within the scope of not impairing the effects of the present invention.
Examples of such additives include saturated fatty acids such as palmitic acid and stearic acid; unsaturated fatty acids such as linolenic acid, linoleic acid, and oleic acid; metal salts thereof (examples of the metal: sodium and potassium); organic acids having a hydroxyl group such as lactic acid and tartaric acid; organic acids having a sulfonic acid group such as alkylsulfonic acids and alkylbenzenesulfonic acid; metal chelating agents; curing agents for curing curable resins; dispersants; film-forming assistants; surface conditioners; plasticizers; antioxidants; and pigments.
Each of these additives may be used alone or in combination of two or more.

The thickness of the conductive layer is not particularly limited as long as it is the same thickness as that of a conventional circuit. However, from the viewpoint of maintaining a desired conductive layer that does not peel off or break even when the substrate with the conductive layer is bent, the thickness is preferably 1 to 1000 μm, more preferably 1 to 200 μm, and even more preferably 1 to 100 μm.
In addition, in the case of the substrate with the conductive layer, a dried or hardened body of the conductive composition may be formed inside the substrate, but even in this case, the thickness of the conductive layer refers to the thickness from the surface of the substrate.

<Method of manufacturing the substrate with conductive layer>
The method for producing the present substrate with a conductive layer is not particularly limited, but preferably includes the steps of coating the substrate with the conductive composition and drying or curing the coated composition.

The method for applying the conductive composition is not particularly limited, and any conventionally known method can be used without limitation. Examples of the method include screen printing, pad printing, flexographic printing, inkjet printing, and gravure printing.
In this coating, it is preferable to coat the conductive layer so that the conductive layer to be formed has a desired shape and thickness.

The conditions for drying or curing the composition are not particularly limited and may be appropriately selected depending on the conductive composition (binder and solvent type) used, and may be dried and/or cured at room temperature, dried and/or cured under heating, or dried and/or cured under light irradiation. Heating and light irradiation may also be combined.
The drying or curing may be carried out under reduced pressure or in an inert gas atmosphere such as a nitrogen gas atmosphere, if necessary.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these.

[Example 1]
A nonwoven fabric made of PTFE nanofibers (thickness: 55 μm, basis weight: 24 g/ ^m2 , average pore size [measured using a Perm-Porometer (CFP-1200-AEL) manufactured by Porous Materials Inc. (average pore size below was also measured in the same manner)]: 2 μm, average fiber diameter: 900 nm, size of main surface: length 100 mm × width 100 mm) was used as the substrate, and conductive ink 1 (manufactured by ThreeBond Co., Ltd., viscosity at 25°C using a rotational viscometer (rotation speed condition: 50 rpm): 20 Pa·s, containing silver particles) was screen-printed on the main surface of the substrate using a screen and a squeegee so that the resulting conductive layer (circuit) had a line width of 0.5 mm, a conductive layer spacing of 1.0 mm, a length of 100 mm and a thickness of 25 μm.
The printed conductive ink 1 was heated at 160° C. for 1 hour to prepare a substrate with a conductive layer.

[Example 2]
A substrate with a conductive layer was prepared in the same manner as in Example 1, except that in Example 1, conductive ink 2 (CR-5200 (manufactured by Kaken Tech Co., Ltd.), viscosity at 25°C using a rotational viscometer (rotation speed condition: 50 rpm): 20 Pa s, containing silver particles) was used instead of conductive ink 1, and the curing conditions were changed to heating at 100°C for 1 hour.

[Example 3]
A substrate with a conductive layer was prepared in the same manner as in Example 1, except that a nonwoven fabric made of PTFE nanofiber (thickness: 72 μm, basis weight: 32 g/m ² , average pore size: 2 μm, average fiber diameter: 900 nm) was used as the substrate.

[Example 4]
A substrate with a conductive layer was prepared in the same manner as in Example 1, except that a nonwoven fabric made of PTFE nanofiber (thickness: 92 μm, basis weight: 40 g/m ² , average pore size: 2 μm, average fiber diameter: 900 nm) was used as the substrate.

[Example 5]
A substrate with a conductive layer was prepared in the same manner as in Example 1, except that, instead of screen printing, a tabletop precision coating device (manufactured by SSI Japan Ltd.) was used to inkjet print conductive ink 1 so that the resulting conductive layer (circuit) had a line width of 0.5 mm, a conductive layer spacing of 1.0 mm, a length of 100 mm, and a thickness of 150 μm.

[Comparative Example 1]
A substrate with a conductive layer was produced in the same manner as in Example 1, except that a PTFE film (VALFLON cutting tape (manufactured by Valqua Corporation), solid film, thickness: 100 μm, size of main surface: length 100 mm × width 100 mm) was used as the substrate.

[Comparative Example 2]
A substrate with a conductive layer was produced in the same manner as in Example 1, except that an expanded PTFE film (sa-PTFE (manufactured by Valqua Corporation), thickness: 25 μm, average pore size: 0.1 μm, size of main surface: length 100 mm × width 100 mm) was used as the substrate.

<Heat resistance>
The shrinkage rate was calculated based on the following formula from the lateral length of the main surface of the substrate (nonwoven fabric made of PTFE nanofibers, PTFE film, or stretched PTFE film) before the conductive ink was applied and the lateral length of the main surface of the substrate with the conductive layer thus prepared.
A shrinkage rate of less than 5% was evaluated as "good," and a shrinkage rate of more than 5% was evaluated as "poor." The results are shown in Table 1.
Shrinkage rate (%)=(lateral length of the main surface of the substrate before the conductive ink is applied−lateral length of the main surface of the substrate with the conductive layer prepared)×100/lateral length of the main surface of the substrate before the conductive ink is applied

<Continuous bending test>
Paper (thickness: 93 μm, 70 g/ ^m2 ) was used as a support for the continuous bending test, and the paper was attached using tape to the side opposite the side to which the conductive layer was attached of the prepared substrate with a conductive layer, to prepare a specimen for the bending test.
Using a bending tester (MIT-D, manufactured by Toyo Seiki Seisakusho, Ltd.), the prepared test specimen was bent 2000 times so that the conductive layer was bent under conditions of a test speed of 90 cpm, a bending angle of 135°, and a curvature radius of 0.38 mm.
The state of the conductive layer before and after bending in this manner was visually confirmed, and the electrical resistance of the conductive layer was measured using SK-6555 (manufactured by Kaise Co., Ltd.) and evaluated based on the following criteria. The results are shown in Table 1.
○: The absolute value of the rate of change in the electrical resistance of the conductive layer before and after the continuous bending test ((1-electrical resistance after continuous bending test) x 100/electrical resistance before continuous bending test) is 50% or less, the conductive layer does not peel off from the substrate, and there are no cracks in the conductive layer. ×: At least one of the following is satisfied: the absolute value of the rate of change in the electrical resistance of the conductive layer before and after the continuous bending test ((1-electrical resistance after continuous bending test) x 100/electrical resistance before continuous bending test) exceeds 50%, the conductive layer peels off from the substrate, or cracks occur in the conductive layer.

<Gurley air permeability>
The Gurley air permeability of the prepared substrate with a conductive layer was measured according to JIS P 8117: 2009 using G-B3C manufactured by Toyo Seiki Seisakusho Co., Ltd. The results are shown in Table 1.
In addition, in Comparative Example 1, since the Gurley air permeability could not be measured due to lack of air permeability, it is indicated as "X" in Table 1.

When the substrate with the conductive layer prepared in the examples was subjected to energy dispersive X-ray analysis (EDX) using an SDD-EMAX x-act (manufactured by Horiba, Ltd.), it was confirmed that the resin of the conductive ink had soaked into the nonwoven fabric. It is believed that the anchor effect caused by this soaking in of the resin made it possible to form the desired conductive layer that does not peel off even after continuous bending tests, even on nonwoven fabric made of PTFE nanofiber, which is originally non-adhesive.

Claims (3)

A method for producing a substrate with a conductive layer, the method comprising the steps of: applying a conductive composition having a viscosity of 1 to 500 Pa·s at 25°C measured with a rotational viscometer (rotation speed condition: 50 rpm) to a substrate that is a woven or nonwoven fabric containing nanofibers made of polytetrafluoroethylene (PTFE); and drying or curing the applied conductive composition,
A method for producing a substrate with a conductive layer, which satisfies the following requirement (1):
Requirement (1): The Gurley air permeability of the substrate with the conductive layer is 10 seconds/100 ml or less. The method for producing a substrate with a conductive layer according to claim 1 , wherein the conductive composition comprises a conductive filler and a thermosetting resin. 3. The method for producing a substrate with a conductive layer according to claim 1, wherein the substrate has a basis weight of 10 to 200 g/ ^m2 before being coated with the conductive composition .